In an effort to improve the overall performance of occupant safety systems, particularly where an air bag is to be deployed, energy management or dissipation systems are being proposed to dissipate energy and reduce the maximum forces being applied to the passenger's chest and to reduce head injuries. The latter is often termed "lowering head injury criteria" or HIC for short. Many of these proposed energy management systems involve large, cumbersome structures that are not easily mounted in the same space as are current seat belt retractor systems. Other systems are very complex and are subject to inconsistent or unpredictable results, such as can occur when metal pieces tear during energy dissipation.
There is a need for an energy management system that will provide consistent known or predictable results of reducing substantially the amount of deflection of the passenger's chest, the maximum G's being experienced, the maximum shoulder load being experienced, etc. It will be appreciated that vehicles have varying parameters because of their size, shape and interior seating arrangements. This results in different spaces between the passenger and a steering wheel, windshield, dashboard, or the like. Different vehicles will have different energy absorption characteristics and different time intervals for deployment to an effective positioning of an air bag, as well as various other parameters that make for different crash characteristics for different vehicles. Because of such different crash characteristics, vehicle manufacturers would prefer an energy management system that can be matched or tuned to their specific needs for each kind of vehicle. This has not heretofore been attained. For example, energy management systems have been suggested that dissipate energy by the tearing of metal or use materials that will not provide consistent, predictable energy dissipation for one particular vehicle's crash characteristics much less be able to be tuned, with suitable adjustments, to a plurality of crash characteristics for different vehicles.
It is desirable to be able to tune the energy dissipation in a manner such that the energy dissipation does not occur until an initial predetermined force level is reached, which usually occurs during the time that the air bag is being deployed and inflated. This initial predetermined force level is hereinafter termed the threshold or onset force level, and it should be adjustable for different vehicles and set to a specific force level, for example, 700 lbs. of tensile force on the shoulder belt. After the reaching of the onset force level, the energy dissipation then begins with some belt protraction as deformation of materials occurs in the energy dissipation system. For vehicles having a small spacing between the passenger and an adjacent portion of a vehicle, it may be desirable to let the shoulder force rise more sharply with time than for other vehicles where there is a larger spacing between the passenger and an adjacent portion of the vehicle. In the latter instance, it may be desirable that greater energy absorption is done initially to avoid a sharp rise in the shoulder belt load, so that the passenger's shoulder belt load is maintained substantially level or constant over the length of shoulder belt protraction. Another variable is the length of belt protraction which the manufacture will allow during energy dissipation, and this appears to range from a low of about six (6) inches to a high of about twenty (20) inches of belt protraction. Another factor or variable is the length of time over which the energy dissipation has to occur. Usually a six-inch belt protraction occurs more quickly than a twenty-inch belt protraction.
Energy absorption systems should be effective to lower the HIC, the shoulder belt loads, the G loads, and chest or sternum deflection. To these ends, they should absorb such energy to decrease and smooth out large, sharp increases of shoulder loads or chest deflections to more lower, known amounts of shoulder belt forces and chest deflections in a known and consistent manner. The preferred energy management system should be able to provide predictable, known energy dissipation data to the vehicle manufacturer with respect to force, time and belt protraction that is tuned to a particular vehicle's crash characteristics.
Preferably, such a system will allow the use of known and proven retractor mechanisms and be relatively simple and inexpensive. Also, the energy dissipation mechanism is preferably small so that the seat belt system can be placed in its usual space and location.